My BLOG about my journey into the invisible world of ultraviolet UV photography, simulated bee, butterfly and animal vision photography and the special lenses, filters and lighting needed to make it work - also in HD video + 3D stereo.

Saturday, January 29, 2011

This is simply a collection of links to tests I have done for various lenses in terms of UV transmission and UV focus shift. Some also contain IR tests. No specific order and no ranking implied. Only lenses tested I own; if one seems to miss, I simply don't have it.

I have been asked, if there is a way to simply determine the needed length of a focusing helicoid to reach infinity focus [when mounting for instance an enlarger lens, or lens without own focusing mount to a camera}.

Yes, it can be determined, if you have the register length ("Auflagemass" in German) for a given length. If not, measurements or an approximation have to be used.

that also means that HLI cannot be negative and has to be at least some 15mm or so (shortest Helicoid I know of; but there is an exception). This also explains why with some lenses infinity focus cannot be reached.

If RLL is not known, the following procedure allows to measure it approximately:

Take a white sheet of paper, a ruler and your lens, hold the lens in front of the white paper in a darkened room and point the lens front with fully open aperture to the outside to a far away bright and contrasty object (can be the sun, but be careful not to burn the paper, or a hill against the sky) at least 100x further away then the focal length of that lens until you get a sharp image on that paper. Now measure the distance from that paper to the flange of the lens (end of the thread or mount (could be bajonet etc.) - not just the physical end of the lens!). This is approximately RLL.

If you want to use that lens for macro shooting, say at 1:1 magnification, then point the lens using the same procedure to a bright lamp (desktop tungsten works well) until you see an projected image which has the same size as the original lamp (us the visible lamp filament for instance (stepping down helps if the image is too bright). Keep that position and repeat the measurement at mentioned above). That gives you the approximation for RLL(1x) at magnification 1x.

Now we get

HL(1x) = RLL(1x) - RLC - AL

where HL(1x) denotes the needed maximum extension of your helicoid and

HR = HL(1x) - HLI is the range your helicoid has to cover when turning from infinity to 1x magnification (you can replace 1x with any wished factor of course). If HR is too long, it has to be replaced with a shorter helicoid and a tube of fixed length (say to reach only 0.5x for instance). [Example, if you would need HR = 50mm and the longest helicoid you can find is 25mm, then add a 25mm tube to reach 50mm]

I hope that was not too complicated...

Here a few images that explain that in a few images when mounting an enlarger lens (here a EL-Nikkor 3.5/63mm to a Nikon D200 camera for infinity).

[click on image to see a larger one]

First let me show how different long helicoids look like (from a astronomer shop):

Enlarger lens (with filter adapter ring to 52mm) with Leica thread mount M39 (also called LTM and is precisely M39 x 26tpi), M39-M42 adapter ring, M42 helicoid (that helicoid has Nikon mount on the rear, usually a M42-Nikon non-infinity adapter ring would have to be added):

all parts assembled (screwed into each other):

Front view (filter side):

Rear view (camera side):

Mounted on camera:

Take that indicative, it may need a much longer helicoid, if the lens has a much longer focal length, like 105mm or 135mm for instance or you don't need it for infinity but for close-up or macro shots.

Today I found a nice flower, a "Stargazer Lilly", so I thought that would be wonderful to show the beauty of that flower using the newly rediscovered use of older (chrome/black) EL-Nikkor enlarger lenses in visible light, but also in invisible UV.

All shots were done at f8, ISO400, 1/160s using Xenon flash, exposure adjusted using flash power control and ND filters. UV shots were done using the Baader-U filter.

[click on image to see a larger one]

Here now a VIS-UV differential using the EL-Nikkor 5.6/80mm:

and yes, quite a nice lens with quite good UV transmission and very little focus shift.

and here using the 5.6/105mm EL-Nikkor:

Quite more focus shift, but also quite good UV transmission.

For comparison here the VIS shot using the EL-Nikkor 5.6/80mm:

and using the 5.6/105mm EL-Nikkor:

Finally now the UV shot using the EL-Nikkor 5.6/80mm:

and using the 5.6/105mm EL-Nikkor:

So, if you look for a cheap lens, have an eye on these pretty good enlarger lenses!

P.S.: the 80mm EL-Nikkor (the older, chrome black full metal type) has an adapter ring on its base with outer M39x26tpi screw mount (Leica enlarger mount). Beneath it is a M25 thread for older #00 shutters. Company Schneider Optics offers adapter rings, if that one should be missing (oder code 92-013251).P.P.S.: the filter thread of that older EL-Nikkor 80mm is 34.5mm, which is pretty uncommon, as me if you need an adapter ring.

[A remark on the 80mm EL-Nikkor, I tried outside and infinity tests with it and unfortunately it seems to have a prominent large UV hotspot which renders it unuseable for that...]

About Me

This is my blog about my film and photographic work in 3D, ultraviolet UV, infrared IR and fluorescence using special lenses and equipment. All text and images carry my copyright and I do not allow to link to or copy / download from my site or any parts thereof without my prior permission.
email me in case of questions or interest in my images (esp. for non-profit orgs) or if you need a complete camera + lens + filter + light set for UV photography:
postmaster AT macrolenses.de